This invention relates to a process of thickening aqueous systems with copolymers, especially emulsion copolymers, to enhancement of such thickening by the addition of surfactants, and to other aspects including coating compositions and other aqueous systems thickened with the polymers.
This application is related to applicant's Ser. No. 101,615, filed Dec. 10, 1979, now abandoned, and corresponding European Patent Publication No. 13,836, dated Aug. 6, 1980, entitled "(Meth)acrylic Acid Emulsion Copolymers for Thickening Purposes". This earlier application discloses emulsion copolymers, and the use thereof as thickeners in aqueous dispersions, of (meth)acrylic acid, and alkyl poly(oxyethylene)(meth)acrylate, and a C.sub.1 -C.sub.4 alkyl(meth)acrylate, and, optionally, a small amount of a polyethylenically unsaturated monomer.
European Patent Publication No. 11,806, dated June 11, 1980, discloses aqueous emulsion polymers which are pH responsive and are prepared by emulsion polymerization of 15-60% of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, 15-80% of an .alpha.,.beta.-ethylenically unsaturated monomer, and 1-30% of a nonionic vinyl surfactant ester, preferably a monovinyl ester such as nonylphenoxy poly(ethyleneoxy).sub.9 ethyl acrylate.
U.S. Pat. No. 4,138,381 discloses a liquid composition useful as a thickening agent in polymeric latices of (A) 50 weight percent of a polymer of units of (1) 10-98% of an unsaturated C.sub.3 -C.sub.6 carboxylic acid, (2) about 1-50% of a C.sub.1 -C.sub.30 alkyl(meth)acrylate, and (3) 1-85% of an ester of the formula ##STR1## where x is 5-80, y is 0-20, R and R.sup.2 are H or CH.sub.3, and R.sup.1 is alkyl or phenyl; and (B) as a solvent for (A), (4) a glycol, or (5) a glycol containing up to 50% of its weight of water; the composition being made by free radical solution polymerization techniques.
U.S. Pat. No. 4,268,641 discloses a normally solid, base-neutralized copolymer having copolymerized therein about 90-99 mole percent of a carboxy-containing ethylenically unsaturated hydrocarbon and about 1-10 mole percent of a nonionic surfactant acrylate having the formula EQU R.sup.1 --(A).sub.x --OC(O)--CR.dbd.CH.sub.2
wherein R is H or CH.sub.3, R.sup.1 is a hydrophobe selected from the group consisting of alkyl--O--, alkyl--NH--, and alkyl--CO--, where alkyl contains 4-30 carbon atoms. A is a divalent radical selected from the group consisting of oxyethylene or oxyalkylene units or mixed oxyalkylene units --OC.sub.n H.sub.2n --.sub.x where n is an integer from 2 to 4 and x is an integer of 5-40, said surfactant acrylate having an HLB (hydrophilic lipophilic balance) value of about 10-19.
Salts of polyacrylic acid and polymethacrylic acid are well known as thickeners for various aqueous systems. A polyacrylic acid obtained by copolymerizing acrylic acid with a small amount (about 0.2 to 1% by weight on the weight of acrylic acid) of diallyl sucrose (U.S. Pat. No. 2,798,053) has also been sold for use as a thickener for many years. These thickening agents are difficult to handle because they are either powders that are slow to dissolve or very viscous aqueous solutions. Adverse effects such as stiffness or water sensitivity also may be imparted to the finished product by the polymeric acid thickener. Still another problem associated with the acid thickeners is their electrolyte sensitivity. The aqueous systems thickened with these thickeners decrease drastically in viscosity upon addition of an electrolyte, such as sodium chloride.
British Pat. No. 870,994 discloses the preparation of aqueous emulsion copolymers of methacrylic acid and a lower (C.sub.1 -C.sub.4)alkyl acrylate which gives good thickening upon neutralization. The copolymer dispersions having a solids concentration of 25 to 50% by weight are low viscosity fluids and are thus readily added directly to systems to be thickened. However, they also have severe electrolyte sensitivity.
Japanese Patent Publication No. 31089/1973, published Sept. 26, 1973, discloses a method for the manufacture of aliphatically unsaturated dicarboxylic esters of the formula EQU R.sub.3 O(O)C--R.sub.1 --C(O)--OCH.sub.2 CH.sub.2 --.sub.m R.sub.2
wherein R.sub.1 denotes the residue of an aliphatically unsaturated discarboxylic acid, R.sub.2 denotes a halogen atom or an organic residue other than a hydroxyl group, R.sub.3 denotes an alkyl, aryl, alkylaryl, aralkyl, or alkoxyalkylene glycol residue, and m an integer not less than 5. Homopolymers of these esters and copolymers with other vinyl compounds having an active double bond are disclosed to be useful in the modification of fibers and plastics and as emulsifiers, dispersants, adhesives and "slidants" (sic).
Japanese Patent Publication No. 64216/1975, published May 31, 1975, discloses a method for the manufacture of an aliphatic unsaturated dicarboxylic esters of the formula EQU R.sub.1 O--CH.sub.2 CH.sub.2).sub.n (O)CR.sub.3 C(O)O--R.sub.2
wherein R.sub.1 denotes an alkyl group, a phenyl group, or an alkylphenyl group, n an integer not less than 5, R.sub.3 denotes a residue of an aliphatic unsaturated dicarboxylic acid and R.sub.2 denotes the residue of a lower alcohol. Homopolymers of these esters and copolymers with vinyl compounds having an active double bond are disclosed to be useful in modifying fibers and plastics as emulsifiers, dispersants, adhesives, and "slidants" (sic). The esters of neither Japanese patent publication are disclosed to be useful as thickeners.
The process of this invention is useful for bodying and suspending various mucilaginous and colloidal gel-like systems such as dentrifices, surgical jellies, creams and ointments, printing paste thickeners, and the like. However, most polyelectrolyte solutions decrease drastically in viscosity upon the addition of electrolytes such as sodium chloride. These prior art thickener methods are ion-sensitive and do not adequately maintain the viscosities of water or organic solvent solutions containing inorganic salts such as sodium chloride, even when a third monomer such as 2-ethylhexyl acrylate or styrene, respectively, is included in the polymer as as suggested by the respective prior art patents.